A
plastic is a type of synthetic or man-made polymer; similar in many ways
to natural resins found in trees and other plants. Webster's Dictionary
defines polymers as: any of various complex organic compounds produced by
polymerization, capable of being molded, extruded, cast into various
shapes and films, or drawn into filaments and then used as textile fibers.

Raw
Materials

Oil
and natural gas are the major raw materials used to manufacture plastics.
The plastics production process begins by heating components of crude oil
or natural gas in a "cracking process." This process results in
the conversion of these components into hydrocarbon monomers such as
ethylene and propylene . Further processing leads to a wider range of
monomers such as styrene, vinyl chloride, ethylene glycol, terephthalic
acid and many others. These monomers are then chemically bonded into
chains called polymers. The different combinations of monomers yield
plastics with a wide range of properties and characteristics.

Plastics

Many
common plastics are made from hydrocarbon monomers. These plastics are
made by linking many monomers together into long chains with a carbon
backbone. Polyethylene, polypropylene and polystyrene are the most common
examples of these. Below is a diagram of polyethylene, the simplest
plastic structure.

Even
though the basic makeup of many plastics is carbon and hydrogen, other
elements can also be involved. Oxygen, chlorine, fluorine and nitrogen are
also found in the molecular makeup of many plastics. Polyvinyl chloride
(PVC) contains chlorine. Nylon contains nitrogen. Teflon contains
fluorine. Polyester and polycarbonates contain oxygen.

Additives

Most
plastics are blended with additives as they are processed into finished
products. The additives are incorporated into plastics to alter and
improve their basic mechanical, physical or chemical properties. Additives
are used to protect plastics from the degrading effects of light, heat, or
bacteria; to change such plastic properties as flow; to provide color; and
to provide special characteristics such as improved surface appearance or
reduced tack/friction.

Plasticizers
are materials incorporated into certain plastics to increase flexibility
and workability. Plasticizers are found in many plastic film wraps and in
flexible plastic tubing, both of which are commonly used in food packaging
or processing. All plastics used in food contact, including the additives
and plasticizers, are regulated by the U.S. Food and Drug Administration
(FDA) to ensure that these materials are safe.

Processing
Methods

There
are several different processing methods used to make plastic products.
Below are the four main methods in which plastics are processed to form
the products that consumers use, such as plastic film, bottles, bags and
other containers.

Extrusion
- Plastic pellets or granules are first loaded into a hopper, then fed
into an extruder, which is a long heated chamber, through which it is
moved by the action of a continuously revolving screw. At the end of the
extruder, the molten plastic is forced out through a small opening or die
to shape the finished product. As the plastic product extrudes from the
die, it is cooled by air or water. Plastic films and bags are made by
extrusion processing.

Injection
molding
- In injection molding, plastic pellets or granules are fed from a hopper
into a heating chamber. A plunger pushes the plastic through the heating
chamber, where the material is softened into a fluid state. At the end of
this chamber, the resin is forced into a cooled, closed mold. Once the
plastic cools to a solid state, the mold opens and the finished part is
ejected. This process is used to make products such as butter tubs, yogurt
containers, closures and fittings.

Blow
molding
- Blow molding is a process in which a molten tube of thermoplastic
material is formed. Using compressed air, the tube is blown to conform to
the interior of a chilled mold that clamps around the tube. This method is
used to make plastic bottles such as milk jugs.

Rotational
Molding
- Rotational molding consists of a closed mold mounted on a machine
capable of rotation on two axes simultaneously. Plastic granules are
placed in the mold, which is then heated in an oven to melt the plastic
Rotation around both axes distributes the molten plastic into a uniform
coating on the inside of the mold until the part is set by cooling. This
process is used to make hollow products, for example large toys or kayaks.

Durables
Vs. Non-Durables

All
types of plastic products are classified within the plastic industry as
being either a durable or non-durable plastic good. These classifications
are used to refer to a product's expected life.

Products
with a useful life of three years or more are referred to as durables.
They include appliances, furniture, consumer electronics, automobiles, and
building and construction materials.

Products
with a useful life of less than three years are generally referred to as
non-durables. Common applications include packaging, trash bags, cups,
eating utensils, sporting and recreational equipment, toys, medical
devices and disposable diapers.

PETE

Polyethylene
Terephthalate (PET or PETE) is clear, tough and has good gas and moisture
barrier properties making it ideal for carbonated beverage applications
and other food containers. The fact that it has high use temperature
allows it to be used in applications such as heatable pre-prepared food
trays. Its heat resistance and microwave transparency make it an ideal
heatable film. It also finds applications in such diverse end uses as
fibers for clothing and carpets, bottles, food containers, strapping, and
engineering plastics for precision-molded parts.

HDPE

High
Density Polyethylene (HDPE) is used for many packaging applications
because it provides excellent moisture barrier properties and chemical
resistance. However, HDPE, like all types of polyethylene, is limited to
those food packaging applications that do not require an oxygen or CO2
barrier. In film form, HDPE is used in snack food packages and cereal box
liners; in blow-molded bottle form, for milk and non-carbonated beverage
bottles; and in injection-molded tub form, for packaging margarine,
whipped toppings and deli foods. Because HDPE has good chemical
resistance, it is used for packaging many household as well as industrial
chemicals such as detergents, bleach and acids. General uses of HDPE
include injection-molded beverage cases, bread trays as well as films for
grocery sacks and bottles for beverages and household chemicals.

PVC

Polyvinyl
Chloride (PVC) has excellent transparency, chemical resistance, long term
stability, good weatherability and stable electrical properties. Vinyl
products can be broadly divided into rigid and flexible materials. Rigid
applications are concentrated in construction markets, which includes pipe
and fittings, siding, carpet backing and windows. PVC's success in pipe
and fittings can be attributed to its resistance to most chemicals,
imperviousness to attack by bacteria or micro-organisms, corrosion
resistance and strength. Flexible vinyl is used in wire and cable
sheathing, insulation, film and sheet, floor coverings, synthetic leather
products, coatings, blood bags and medical tubing.

LDPE

Low
Density Polyethylene (LDPE) is predominantly used in film applications due
to its toughness, flexibility and transparency. LDPE has a low melting
point making it popular for use in applications where heat sealing is
necessary. Typically, LDPE is used to manufacture flexible films such as
those used for dry cleaned garment bags and produce bags. LDPE is also
used to manufacture some flexible lids and bottles, and it is widely used
in wire and cable applications for its stable electrical properties and
processing characteristics.

PP

Polypropylene
(PP) has excellent chemical resistance and is commonly used in packaging.
It has a high melting point, making it ideal for hot fill liquids.
Polypropylene is found in everything from flexible and rigid packaging to
fibers for fabrics and carpets and large molded parts for automotive and
consumer products. Like other plastics, polypropylene has excellent
resistance to water and to salt and acid solutions that are destructive to
metals. Typical applications include ketchup bottles, yogurt containers,
medicine bottles, pancake syrup bottles and automobile battery casings.

PS

Polystyrene
(PS) is a versatile plastic that can be rigid or foamed. General purpose
polystyrene is clear, hard and brittle. Its clarity allows it to be used
when see-throughability is important, as in medical and food packaging, in
laboratory ware, and in certain electronic uses. Expandable Polystyrene
(EPS) is commonly extruded into sheet for thermoforming into trays for
meats, fish and cheeses and into containers such as egg crates. EPS is
also directly formed into cups and tubs for dry foods such as dehydrated
soups. Both foamed sheet and molded tubs are used extensively in take-out
restaurants for their lightweight, stiffness and excellent thermal
insulation.

Other
Plastics

There
are many other plastics beyond the most common ones described above, for
example Nylon, ABS copolymers and Polymethyl Methacrylate.

Whether
you are aware of it or not, plastics play an important part in your life.
Plastics' versatility allow it to be used in everything from car parts to
doll parts, from soft drink bottles to the refrigerators they get stored
in. From the car you drive to work in to the television you watch when you
get home, plastics help make your life easier and better. So how is it
that plastics have become so widely used? How did plastics become the
material of choice for so many varied applications?

The
simple answer is that plastics can provide the things consumers want and
need. Plastics have the unique capability to be manufactured to meet very
specific functional needs for consumers. So maybe there's another question
that's relevant: What do I want? Regardless of how you answer this
question, plastics can probably satisfy your needs.